cfd applications in nuclear reactor safety · 2019-11-27 · cfd applications in nuclear reactor...
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CFD Applications in Nuclear Reactor Safety
Dipl.-Ing. Martina Scheuerer
Gesellschaft für Anlagen- und Reaktorsicherheit (GRS)
Forschungsgelände, Garching
Jahrestagung Kerntechnik, 7 May 2015
Overview
Motivation
Networks
Application areas
• Validation
• Industrial applications
Best practices
• OECD Best Practice Guidelines
Summary & outlook
CFD - Motivation
Simulation tasks
• Quantification of safety margins
• Assessment of performance increases
• New strategies for core loading & management
CFD applications
• Multi-dimensional phenomena
• Complement to system codes
CFD development needs
• Physics – Turbulence, heat transfer, combustion, multiphase flows, …
• Numerics - Speed
CFD Networks in Nuclear Reactor Safety
German CFD Network
• http://cfd.grs.de
International OECD Task Group
• www.oecd-nea.org/nsd/csni/cfd
Objectives:
• Best practice guidelines
• Assessment of CFD codes for NRS
• CFD4NRS workshops & benchmarks
Nuclear Reactor CFD
Primary system & core
Secondary system
Containment & sump
Emission
Deposition
Storage, …
Primary System & Core
Quantification of safety margins
Life extension
• Material fatigue
• Pressurised thermal shocks
Re-criticality
• Boron dilution & mixing
• Ballooning
Fuel behaviour
• Neutron kinetics & CFD coupling
Primary Circuit & Core – Model Requirements
Turbulence
• Unsteady-state mixing
• Buoyancy & stratification
Energy transfer
• Convection & conduction conjugate heat transfer
Multi-phase flows
• Bubbles free surfaces
• Condensation & boiling
Multi-physics & multi-scale
• Fluid-thermal & fluid-structure
• Neutron kinetics & CFD
• System & field ATHLET-2-CFD
Containment & Sump
Discharges of primary or secondary circuits
Hydrogen distribution in containments
Recombiners
Condensation
Detonation & deflagration
Containment integrity
Containment & Sump – Model Requirements
Turbulence
• Unsteady-state mixing
• Buoyancy & stratification
Energy transfer
• Convection & conducation conjugate heat transfer
• Radiation
Multi-phase flows
• Free-surface flows
• Condensation
Chemical reactions
• Combustion deflagration detonation
• Recombiners
Multi-physics
• Fluid-structure
Nuclear Reactor Safety & CFD Quality
• Use of CFD results for quantitative safety-critical analyses
Objective
• Accuracy
• Reliability
• Robustness
• Fault tolerance
Requirements • Quantification of numerical
errors
• Estimation of model errors
• Uncertainty quantification
• Knowledge management
• Competence management best practices
Quality
Best Practice Guidelines
https://www.oecd-nea.org/nsd/docs/2007/csni-r2007-5.pdf
Requirement specification
• Cost & effort
• Accuracy
• Validation or “production”
Best Practice Guidelines
• Procedures & processes
• Checklists
Knowledge management
• Education
• Awareness
Best Practice Guidelines - Elements
Model selection
Geometry model - domain
Grid – model requirements &
quality
Initial & boundary conditions – uncertainties
Material properties - uncertainties
Simulation – HPC, …
Error quantification – iteration,
discretisation, model, …
Uncertainty analysis – sensitivities &
robustness
Documentation & knowledge
management
Best Practice Guidelines - Elements
Model selection
Geometry model
Grid
Initial & boundary conditions
Material properties
Simulation
Error quantification
Uncertainty analysis
Documentation
Best Practice Guidelines: Grid Generation
Scalable grids
Grid angles > 20° and < 160° (accuracy, convergence)
Expansion ratios < 1.5 …2
Aspect ratios – f(solution algorithm)
Turbulence model requirements
Grid lines aligned with streamlines walls
Capture physics based on experience (shear layers, free surfaces, …)
Best Practice – Turbulence Model Recommendations
URANS
• SST model
• Automatic wall functions
Scale-resolving hybrid
• SAS
• DDES
• …
• ZLES
Scale-resolving
• LES
• WMLES
• Proven technology • Consistency • Diversity consolidation
Best Practice – Example
Large Scale Test Facility (LSTF)
• Height = 4-loop 1100 MW Westinghouse PWR
• Volume scale: 1:48
• Scaled nominal power: 2 %
OECD/NEA ROSA V
• Buoyancy-driven stratified flow
• ECC injection in cold leg
• Natural circulation condition
• Temperature stratification
Source: T. Yonomoto 2005, JAERI
BPG – Model, Geometry, Initial & Boundary Conditions
Model
• URANS – SST & RSM
Geometry
• Half model for BPG
• Full model for production
Initial condition
• Steady-state natural circulation
Boundary conditions @ cold legs and ECC nozzle
• Inlet mass flow rates
• Inlet temperature
• Pressure @ downcomer bottom
BPG: Numerical Grids
Coarse mesh
• 1 million elements
Medium mesh
• 5 million elements
Fine mesh
• 8 million elements
BPG: Discretisation Error
Influence of grid size & time step
Compromise between accuracy & computational
effort
Error Estimation Large Problem Sizes
Reactor system
• Grid: 20 million elements
• 1000 s real time
Solution
• Document uncertainties
Research
• Error-adaptive schemes
• HPC
• Discretisation schemes
• Solution algorithms
• Coupling CFD & system codes
Summary and Outlook
Promising technologies
Hybrid scale-resolving turbulence models
“Baseline” multi-phase flow models
HPC System-2-field coupling Multi-physics
Simulation requirements
Accuracy, efficiency, robustness Quality Best practice guidelines
Application areas
Primary system … containment … storage
CFD in NRS
Higher accuracy & detail requirements Increased use